The present invention relates to a process for the preparation of polyether ester polyols starting from fatty acid esters and starter compounds having Zerewitinoff-active hydrogen atoms, and to their use in the production of rigid or foamed polyurethane materials.
Polyols based on renewable raw materials, such as, for example, fatty acid triglycerides, sugars, sorbitol, glycerol and dimers of fatty acid alcohols, are already being used in different ways as starting materials for the production of materials based on polyurethane. It is expected that the use of such compounds will increase further in the future because products from renewable sources have a positive influence on the ecological balance and, at the same time, the availability of petrochemical-based raw materials will decrease in the medium- to long-term.
The poor solubility of sugars, glycerol and sorbitol and also of oligo- or poly-saccharides in other polyether or polyester polyols which are conventionally used in polyurethane chemistry stands in the way of their increased use as polyol components in polyurethane formulations. Moreover, these substances impart very high OH numbers to the polyol component, even when they are used in small amounts, because they contain a plurality of hydroxyl groups.
Fatty acid triglycerides are obtained in large amounts from renewable sources and therefore form an advantageous basis for polyurethane raw materials according to the teaching of EP 1923417 A1. In formulations for the production of rigid foams, this class of compound is distinguished by strongly increasing the solubility of hydrocarbon-based foaming agents.
Pentaerythritol, sugars and other oligo- and poly-saccharides and sugar alcohols such as mannitol or sorbitol generally have melting points which are above the reaction temperature for the preparation of polyether ester polyols or decompose before the melting point is reached. Where such compounds are used according to the process of EP 1923417 A1 together with fatty acid esters for alkoxylation with alkylene oxides, the reaction is difficult to start because the starter compounds are only soluble with difficulty in the reaction mixture at the beginning of the alkylene oxide addition phase. The pressure in the reactor thus increases and the safety-related pressure limits of the reactor can easily be exceeded. In order to ensure that the reaction proceeds safely, the alkylene oxides must therefore be metered into the reaction mixture very slowly or with interruptions.
An object of the present invention was, therefore, to provide a process for the preparation of polyether ester polyols which ensures that the alkylene oxides metered in are absorbed smoothly and can therefore be added continuously. In particular, this process is to be suitable for the preparation of polyether ester polyols based on starter compounds having a melting point above the conventional reaction temperature, that is to say having a melting point above 100° C., or for the preparation of polyether ester polyols based on starter compounds that tend to decompose at the conventional reaction temperature.
The continuous metered addition of the alkylene oxides should be carried out such that the safety-related pressure limits are not exceeded. These are, of course, governed by the apparatus-related conditions prevailing in an individual case; preferably, the process is generally carried out in a pressure range from 1 mbar to 10 bar, the pressure range from 1 mbar to 4 bar being particularly preferred.
A further object of the present invention was to achieve the objects mentioned hereinbefore and at the same time to retain the advantageous properties of the processes known from the prior art for the common reaction of fatty acid esters and alkylene oxides with starter compounds. In particular, it is to be ensured that the fatty acid esters are incorporated fully into the polyether ester polyols that are formed. In addition, the polyether ester polyols prepared by the process according to the invention are to be suitable for the production of rigid polyurethane foam formulations with which rapidly demouldable rigid foams can be obtained. Moreover, the polyether ester polyols obtainable by the process according to the invention are to improve the absorption capacity of the foam formulations for hydrocarbon-based foaming agents.
A further object of the present invention was to provide a process for the preparation of polyether ester polyols in which the starter compounds having Zerewitinoff-active hydrogen atoms are incorporated as fully as possible into the polyether ester polyol; in particular, more than 99 wt. % of the starter compounds are to be incorporated into the polyether ester polyol.